When docking two vehicles at sea, there are six degrees of freedom of motion: roll, pitch, yaw, heave, surge and sway. Motion restriction between the two vehicles can be achieved using a rigid towing structure, such as a steel A-frame. However, a rigid towing structure does not have a satisfactory safety level since it lacks flexibility during attachment.
Current tow cable designs used at sea permit too much motion to make timely hard connections possible or easily automated. For example, FIG. 1 illustrates a first or docking vehicle 2 which in the illustrated example can be a Remote Multi-Mission Vehicle (RMMV) such as an Autonomous Unmanned Vehicle (AUV), an Unmanned Surface Vehicle (USV), an Unmanned Underwater Vehicle (UUV), a manned vehicle such as manned submersible, or the like. The docking vehicle 2 is shown being towed by a second or receiving vehicle 4 (only partially illustrated) using one or more conventional cables 6 such as ropes, chains or the like.
Due to the flexibility of the cable 6, unless the docking vehicle 2 is actively towed, the cable 6 permits fore and aft motions A of the docking vehicle 2 relative to the receiving vehicle 4. In addition, the cable 6 permits the docking vehicle to swing along the axis B relative to the vehicle 4. Therefore, with a conventional cable 6, collisions are a serious risk with at-sea docking and can result in damage to vehicles, loss of material, or even loss of life. Similar relative motions and resultant dangers are present when attaching any two vehicles including land vehicles, space vehicles, sea vehicles and the like.